Imaging device and method for a bonding apparatus

ABSTRACT

An imaging device and method of a bonding apparatus in which the imaging device includes: a high-magnification optical system having first and second high-magnification optical paths that extend to a common imaging plane through a high-magnification lens and have different optical path lengths from the high-magnification lens to the common imaging plane correspondingly to multiple subject imaging ranges which are at different distances from the high-magnification lens; a shutter for opening one of the two high-magnification optical paths and closing the other one; and a low-magnification optical system having a low-magnification optical path that extends to an imaging plane through a low-magnification lens and having a field of view wider than those of the high-magnification optical paths. The imaging element on the imaging plane in the high-magnification optical system images semiconductor chips, while the imaging element on the imaging plane in the low-magnification optical system images a lead frame.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application calms priority under 35 USC 119 from Japanese PatentApplication No. 2007-152642, the disclosure of which is incorporated byreference herein.

BACKGROUND OF THE INVENTION

The present invention relates to a structure of an imaging device for abonding apparatus and to an imaging method using the imaging device fora bonding apparatus.

The assembling of semiconductor devices includes: a die bonding step ofbonding semiconductor chips cut out from a wafer on a lead frame orsubstrate; and a wire bonding step of wire-connecting pads on thesemiconductor chips bonded on the lead frame or substrate to the leadframe or leads on the substrate. The wire bonding provides wireconnections between the pads and leads by pressing a bonding tool suchas a capillary with a wire inserted therethrough at a first bondingpoint on a lead or pad, thus bonding the wire with an ultrasonicvibration, and then looping the wire from the first bonding point towarda corresponding pad or lead, and pressing and bonding the wire at asecond bonding point on the corresponding pad or lead with an ultrasonicvibration. Since wire bonding is required to provide precise connectionsbetween pads and leads that have small areas, it is necessary to pressthe leading end of a bonding tool such as a capillary precisely on thepads and leads.

However, the bonding accuracy between a lead frame or substrate andsemiconductor chips is often varied, which can result in a deteriorationin bonding quality unless the positional relationship is corrected.

To address this issue, it has been practiced that before wire bonding,pads and leads are imaged using a camera, the image is then processed toread a particular pattern as a binary image, and the positions of thepads and leads are detected and corrected accordingly.

However, if the difference in level between the surfaces ofsemiconductor chips and leads is increased with an increase in the sizeof the semiconductor device and the number of pins, the pads on thesurfaces of the semiconductor chips and the lead frame or the leads onthe surface of the substrate can not be included concurrently within thedepth-of-field of the camera, resulting in defocusing either of theimages to make position detection impossible.

For this reason, there has been a proposed method of providing twocameras that are focused, respectively, on chips and leads in the samefield of view, imaging the chips and leads using the respective cameras,and performing position detection based on the images (see PatentDocument 1, for example).

There has also been a proposed method of providing a shutter forswitching optical paths in an optical system having two optical pathswith different optical path lengths that include chips and leads withintheir respective depth-of-fields, and switching the optical paths by theshutter to image the chips and leads using a common camera through eachoptical path (see Patent Document 2, for example).

There has further been a proposed method of imaging semiconductor chipsand leads at mutually different heights using three cameras (refer toPatent Document 3, for example).

[Patent Document 1] Japanese Patent Application Unexamined PublicationDisclosure No. 2-301148

[Patent Document 2] Japanese Patent No. 3272640

[Patent Document 3] Japanese Patent Application Unexamined PublicationDisclosure No. 5-332739

However, multilayer semiconductor devices in which semiconductor chipsare stacked in multiple layers on a lead frame have started to beproduced in the recent demand for capacity increase and space saving insemiconductor devices. Such stacking semiconductor chips in multiplelayers increase the difference in level in the height direction of thesemiconductor chips, requiring imaging devices available for the moreincreased difference in level in the height direction. In addition, thedemand for space saving makes the pitch as well as the size of the padson the semiconductor chips smaller. This requires an improved imagingaccuracy to detect the positions of the pads accurately before wirebonding, requiring high-magnification imaging devices.

In contrast, the dimensional accuracy of lead frames is lower than thatof semiconductor chips, and leads are often arranged in substantiallyvaried positions. It is, therefore, necessary to image all the leadsconnected to the pads on the semiconductor chips to detect the positionsof all the leads before wire bonding between each semiconductor chip andlead frame.

Trying to address such demands with the related arts disclosed in PatentDocuments 1 to 3 requires multiple higher-magnification and small-fieldoptical systems to be combined, where such higher-magnification opticalsystems would narrow the field of view imagable in each optical system.However, since the leads are provided around the semiconductor chips,the imaging area for detecting the positions of the leads becomeslarger. Imaging such a large area using a small-field optical system foreach semiconductor chip or each layer would take a long time to detectthe positions of the leads, resulting in a problem that high-speed wirebonding cannot be achieved. On the contrary, combining multiplelower-magnification optical systems using the related arts disclosed inPatent Documents 1 to 3 would not take a long time to detect thepositions of the leads, but the imaging accuracy for pads cannot be sohigh, resulting in a problem that the positions of pads arranged at asmall pitch can not be detected accurately.

In other words, the demands for accurate imaging of semiconductor chipshaving a great difference in level in the height direction and thedemands for reduction in time for imaging a lead frame to achievehigh-speed wire bonding conflict with each other. The related artsdisclosed in Patent Documents 1 to 3 cannot meet such conflictingdemands.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to accurately imagesemiconductor chips having a great difference in level in the heightdirection and to reduce the time for imaging a lead frame.

According to an exemplary embodiment of the present invention, animaging device for a bonding apparatus for imaging an imaging subjectand multi-layered semiconductor chips mounted on the imaging subject isconfigured to include:

-   -   a first optical system having a plurality of optical paths that        extend to a common imaging plane through a first lens and have        different optical path lengths from the first lens to the common        imaging plane correspondingly to a plurality of subject imaging        ranges at different distances from the first lens;    -   an optical path switching means for opening one of the plurality        of optical paths in the first optical system and closing another        one of the optical paths;    -   a second optical system branching from the first optical system        on the subject side of the first lens and having an optical path        that extends to an imaging plane through a second lens with a        lower magnification than the first lens, the second optical        system having a field of view wider than that of the first        optical system;    -   a first imaging element provided on the common imaging plane in        the first optical system to image each layer of the        multi-layered semiconductor chips mounted on the imaging        subject; and    -   a second imaging element provided on the imaging plane in the        second optical system to image the imaging subject.

In this imaging device of the present invention, the above-describedimaging subject is one of a lead frame and a substrate.

According to another exemplary embodiment of the present invention, animaging device for a bonding apparatus for imaging imaging subject andmulti-layered semiconductor chips mounted on the imaging subject isconfigured to include:

-   -   a first optical system having a plurality of optical paths that        extend to a common imaging plane through a subject side of the        lens and a first imaging plane lens and have different optical        path lengths from the first subject side of the lens to the        common imaging plane correspondingly to a plurality of subject        imaging ranges at different distances from the subject side of        the lens;    -   an optical path switching means for opening one of the plurality        of optical paths in the first optical system and closing another        one of the optical paths;    -   a second optical system branching from the first optical system        between the subject side of the lens and the first imaging plane        lens and having an optical path that extends to an imaging plane        through a second imaging plane lens having a lower total        magnification with the subject side of the lens than the first        imaging plane lens the second optical system having a field of        view wider than that of the first optical system;    -   a first imaging element provided on the common imaging plane in        the first optical system to image each layer of the        multi-layered semiconductor chips mounted on the imaging        subject; and    -   a second imaging element provided on the imaging plane in the        second optical system to image the imaging subject.

In this imaging device of the present invention as well, theabove-described imaging subject is one of a lead frame and a substrate.

In the imaging devices for a bonding apparatus according to the presentinvention, the optical path switching means is preferably configured toswitch the plurality of optical paths in accordance with a heightposition of each layer of the multi-layered semiconductor chips to beimaged. The first optical system preferably has an optical path lengthadjustment means installed in each optical path between the firstimaging plane lens and each imaging plane, and this optical path lengthadjustment means is positioned variably in the direction along eachoptical path. The optical path length adjustment means is preferably anoptical path length adjustment lens, the optical path length adjustmentlens is made any one of a light transmitting glass, a light transmittingplastic, and a light transmitting ceramic.

According to another exemplary embodiment of the present invention, animaging method for imaging imaging subject and multi-layeredsemiconductor chips mounted on the imaging subject using an imagingdevice for a bonding apparatus is configured to include the steps of:

-   -   providing an imaging device for a bonding apparatus, the imaging        device including:        -   a first optical system having a plurality of optical paths            that extend to a common imaging plane through a first lens            and have different optical path lengths from the first lens            to the common imaging plane correspondingly to a plurality            of subject imaging ranges at different distances from the            first lens,        -   an optical path switching means for opening one of the            plurality of optical paths in the first optical system and            closing another one of the optical paths,        -   a second optical system branching from the first optical            system on the imaging plane side of the first lens and            having an optical path that extends to an imaging plane            through a second lens with a lower magnification than the            first lens, the second optical system having a field of view            wider than that of the first optical system, and        -   a first imaging element provided on the common imaging plane            in the first optical system and a second imaging element            provided on the imaging plane in the second optical system;    -   a lead image imaging step of scanning the field of view of the        second optical system on the imaging subject to cause the second        imaging element provided on the imaging plane in the second        optical system to image the imaging subject including leads        around an entire circumference of the multi-layered        semiconductor chips; and    -   a semiconductor chip imaging step of, using the first imaging        element in the first optical system imaging each layer of the        multi-layered semiconductor chips provided on the imaging plane        in the first optical system through the one optical path in the        first optical system that is opened by the optical path        switching means in accordance with a height position of each        layer of the multi-layered semiconductor chips.

In this imaging method of the present invention, the above-describedimaging subject is one of a lead frame and a substrate.

According to another exemplary embodiment of the present invention, animaging method for imaging imaging subject and multi-layeredsemiconductor chips mounted on the imaging subject using an imagingdevice for a bonding apparatus is configured to include the steps of:

-   -   providing an imaging device for a bonding apparatus, the imaging        device including:        -   a first optical system having a plurality of optical paths            that extend to a common imaging plane through a subject side            of the lens and a first imaging plane lens and have            different optical path lengths from the first imaging plane            lens to the common imaging plane correspondingly to a            plurality of subject imaging ranges at different distances            from the subject side of the lens,        -   an optical path switching means for opening one of the            plurality of optical paths in the first optical system and            closing another one of the optical paths,        -   a second optical system branching from the first optical            system between the subject side of the lens and the first            imaging plane lens and having an optical path that extends            to an imaging plane through a second imaging plane lens            having a lower total magnification with the subject side of            the lens than the first imaging plane lens, the second            optical system having a field of view wider than that of the            first optical system, and        -   a first imaging element provided on the common imaging plane            in the first optical system and a second imaging element            provided on the imaging plane in the second optical system;    -   a lead image imaging step of scanning the field of view of the        second optical system on the imaging subject to cause the second        imaging element provided on the imaging plane in the second        optical system to image the imaging subject including leads        around an entire circumference of the multi-layered        semiconductor chips; and    -   a semiconductor chip imaging step of, using the first imaging        element in the first optical system, imaging each layer of the        multi-layered semiconductor chips provided on the imaging plane        in the first optical system through the one optical path in the        first optical system that is opened by the optical path        switching means in accordance with a height position of each        layer of the multi-layered semiconductor chips.

In this imaging method of the present invention as well, theabove-described imaging subject is one of a lead frame and a substrate.

The present invention exhibits an advantageous effect that semiconductorchips with a great difference in level in the height direction can beimaged accurately and the time for imaging the lead frame and thesubstrate can be reduced.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a perspective view of a wire bonder having an imaging devicefor bonding apparatus according to an exemplary embodiment of thepresent invention;

FIG. 2 is a perspective view of the imaging device according to anexemplary embodiment of the invention;

FIG. 3 is an illustrative view showing the configuration of opticalsystems in the imaging device for bonding apparatus according to anexemplary embodiment of the invention;

FIG. 4 is an illustrative view showing a displacement of the focusposition of a lens;

FIG. 5 is an illustrative view showing subject imaging ranges in theimaging device for bonding apparatus according to an exemplaryembodiment of the invention;

FIG. 6 is an illustrative view showing fields of view in the imagingdevice for bonding apparatus according to an exemplary embodiment of theinvention;

FIG. 7 is an illustrative view showing the field of view of ahigh-magnification optical system in the imaging device for bondingapparatus according to an exemplary embodiment of the invention;

FIG. 8 is an illustrative view showing the field of view of alow-magnification optical system in the imaging device for bondingapparatus according to an exemplary embodiment of the invention;

FIG. 9 is an illustrative view showing the configuration of opticalsystems in an imaging device for bonding apparatus according to anotherexemplary embodiment of the invention; and

FIG. 10 is an illustrative view showing the configuration of opticalsystems in an imaging device for bonding apparatus according to stillanother exemplary embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Exemplary embodiments when the present invention is applied to a wirebonder will hereinafter be described in detail with reference to theaccompanying drawings. In the following descriptions, the feeddirection, width direction, and height direction of a lead frame 61 aredefined, respectively, as X, Y, and Z directions.

As shown in FIG. 1, a wire bonder 10 includes a Z-direction drivemechanism 18 installed in a bonding head 11 that is mounted on an X-Ytable 12 to be movable freely in the X and Y directions. The Z-directiondrive mechanism 18 is equipped with an ultrasonic horn 13 and a clamper15, and a capillary 14 is fixed to the leading end of the ultrasonichorn 13. A wire 16 is inserted through the capillary 14, the wire 16being supplied from a spool 17. In addition, an imaging device 21 forbonding apparatus is fixed to the bonding head 11.

Guide rails 81 a and 81 b for guiding the lead frame 61 withsemiconductor chips 63 mounted thereon in a die bonding step and abonding stage 83 for providing a vacuum to cause the lead frame 61 tostick thereto are attached to a frame (not shown in the drawing) of thewire bonder 10.

The wire bonder 10 is adapted to detect the positions of thesemiconductor chips 63 and the lead frame 61 based on images taken bythe imaging device 21, drive the X-Y table 12 so that the capillary 14is positioned over each pad on the semiconductor chips 63, operate theZ-direction drive mechanism 18 to drive the capillary 14 in the Zdirection that is fixed to the leading end of the ultrasonic horn 13,and bond the wire 16, which is inserted through the capillary 14,between each pad on the semiconductor chips 63 and each lead on the leadframe 61.

After bonding between a pad on one semiconductor chip 63 and a lead onthe lead frame 61, the wire bonder 10 drives the X-Y table 12 so thatthe capillary 14 is positioned over the next pad to bond the wire 16between each pad and lead, as in the case described above. Then, if allthe pads on one set of semiconductor chips 63 have completely beenconnected to leads on the lead frame 61 by wires 16, the lead frame 61is carried so that the next set of semiconductor chips 63 are brought tothe bonding position. The imaging device 21 images the semiconductorchips 63 and the lead frame 61 to position the capillary 14 for wirebonding based on the images obtained.

As shown in FIG. 2, the imaging device 21 includes: an introductionsection 22 for introducing light from the subject semiconductor chips 63or lead frame 61 therethrough; a tubular framework 23 incorporatingoptical components such as lenses and mirrors to guide light incidentthrough the introduction section 22; and cameras 24, 25, and 26 thatinclude imaging elements attached to the tubular framework 23 to receivelight passing through the tubular framework 23.

As shown in FIG. 3, the imaging device 21 has a high-magnificationoptical system as a first optical system and a low-magnification opticalsystem as a second optical system. The high-magnification optical systemincludes a first high-magnification optical path 51 extending from thesubject semiconductor chips 63 or lead frame 61 to an imaging plane 36through the introduction section 22, a half mirror 41, ahigh-magnification lens 34, a half mirror 42 a, a shutter 90 as opticalpath switching means, and a half mirror 42 b; and a secondhigh-magnification optical path 52 extending from the subjectsemiconductor chips 63 or lead frame 61 to the common imaging plane 36through the introduction section 22, half mirror 41, high-magnificationlens 34, reflected at the half mirror 42 a to branch from the firsthigh-magnification optical path 51, reflected at a mirror 43 a to passthrough the shutter 90, and reflected at a mirror 43 b and the halfmirror 42 b to join the first high-magnification optical path. Thelow-magnification optical system includes a low-magnification opticalpath 53 extending from the subject semiconductor chips 63 or lead frame61 to an imaging plane 38 through the introduction section 22, reflectedat the half mirror 41 on the subject side of the high-magnification lens34 to branch from the high-magnification optical system, and reflectedat a mirror 44 to pass through a low-magnification lens 35. The shutter90 includes a blade 92 for opening one of the first and secondhigh-magnification optical paths 51 and 52 and closing the other one anda motor 91 for rotating the blade 92. The motor 91 is adapted to rotatethe blade 92 so that one of the first and second high-magnificationoptical paths 51 and 52 can be used for imaging. The optical pathswitching means is not restricted to such a shutter 90 in which themotor 91 rotates the blade 92 for switching the optical paths, but canbe arranged so that electro-optical members with refractive indicesvariable by voltage application thereto are provided in the respectivehigh-magnification optical paths 51 and 52 to be operative in such amanner that one is opened while the other is closed or can be a liquidcrystal shutter, as long as capable of switching the first and secondhigh-magnification optical paths 51 and 52. The common imaging plane 36and the imaging plane 38 are provided, respectively, with a commonimaging element 31 and an imaging element 33 for converting imagesprovided on the respective imaging planes 36 and 38 into electricalsignals. The imaging elements 31 and 33 are each constituted by a CCD(Charge-Coupled Device) and/or a CMOS (Complementary Meta-OxideSemiconductor) element, etc., including a great number of pixels,capable of converting and outputting images into electrical signals foreach pixel. The high- and low-magnification lenses 34 and 35 each canalso be a single lens or a group of lenses in which multiple lenses arecombined to correct aberration.

The distance from the high-magnification lens 34 to the imaging plane 36in the second high-magnification optical path 52 is greater than thedistance from the high-magnification lens 34 to the imaging plane 36 inthe first high-magnification optical path 51. Therefore, the secondhigh-magnification optical path 52 has a focus position where thedistance from the high-magnification lens 34 to the subjectsemiconductor chips 63 is smaller than the distance from thehigh-magnification lens 34 to the subject semiconductor chips 63 in thefirst high-magnification optical path 51.

The relationship between the distance between a lens and an imagingplane and the distance between the lens and an imaging subject will bedescribed with reference to FIG. 4.

As shown in FIG. 4, for the lens L, there is a relationship 1/f+1/S=1/S′wherein the distance from the lens L to a subject focus position A₁ isS, the distance from the lens L to an imaging plane B₁ is S′, and f isthe focal distance of the lens L. Therefore, if the distance from thelens L to an imaging plane B₂ on the imaging plane side of the lens L isgreater by dS′ than the distance S′ from the lens L to the imaging planeB₁, the distance from the lens L to a focus position A₂ on the subjectside lens L becomes smaller by dS than the distance S from the lens L tothe focus position A₁. Here, the “focus position” means a position wherean imaging subject therein is imaged on an imaging plane with beingfocused. In other words, the lens L has a property that the greater thedistance between the lens and the imaging plane on the imaging planeside of the lens L, the smaller the distance between the lens and thefocus position on the subject side lens L. This allows the focusposition of the lens L to be adjusted by adjusting the distance betweenthe lens L and the imaging plane on the imaging plane side of the lensL.

Based on the above-described operating principle of the lens L, as seenfrom FIG. 5, the second high-magnification optical path 52, in which thedistance from the high-magnification lens 34 (corresponding to the lensL) to the imaging plane 36 (see FIG. 2) is greater than the distancefrom the high-magnification lens 34 to the imaging plane 36, has a focusposition A₂ where the distance from the high-magnification lens 34 tothe subject semiconductor chips 63 is smaller than in the firsthigh-magnification optical path 51. In contrast, the firsthigh-magnification optical path 51, in which the distance from thehigh-magnification lens 34 to the imaging plane 36 (see FIG. 2) issmaller than the distance from the high-magnification lens 34 to theimaging plane 36, has a focus position A₁ where the distance from thehigh-magnification lens 34 to the subject semiconductor chips 63 isgreater than in the second high-magnification optical path 52. It shouldbe noted that in FIG. 5, optical systems other than the lenses 34 and 35and the optical paths 51, 52, and 53 are omitted.

In the multilayer semiconductor device shown in FIG. 5, three layers ofsemiconductor chips 63 a, 63 b, and 63 c are stacked and mounted on thelead frame 61. Pads 64 a, 64 b, and 64 c on the respective multi-layeredsemiconductor chips 63 a, 63 b, and 63 c and corresponding leads 62 a,62 b, and 62 c on the lead frame 61 are connected with each other bywires 16. Since the semiconductor chips 63 a, 63 b, and 63 c have theirrespective thicknesses, the pads 64 a, 64 b, and 64 c thereon have theirrespective different levels in the Z direction, i.e., the heightdirection. In contrast, the leads 62 a, 62 b, and 62 c, which are formedon the surface of the lead frame 61, have little differences in level inthe Z direction, i.e., the height direction.

The first high-magnification optical path 51 has a focus position A₁where the distance from the high-magnification lens 34 is greater thanin the second high-magnification optical path 52, while the secondhigh-magnification optical path 52 has a focus position A₂ where thedistance from the high-magnification lens 34 is smaller than in thefirst high-magnification optical path 51. The distance between the focuspositions A₁ and A₂ is dZ. In contrast, the high-magnification lens 34has a depth-of-field D within which imaging subjects can be imaged withbeing focused. Thus, in the first high-magnification optical path 51,imaging subjects can be imaged on the common imaging plane 36 with beingfocused within the depth-of-field D centering on the focus position A₁in the direction along the first high-magnification optical path 51,that is, in the Z direction, i.e., the height direction. Thedepth-of-field D centering on the focus position A₁ provides a subjectimaging range 66 in the first high-magnification optical path 51, andthe common imaging element 31 for the first and secondhigh-magnification optical paths 51 and 52 can image imaging subjectswithin the subject imaging range 66. In the second high-magnificationoptical path 52, imaging subjects can also be imaged on the imagingplane 36 with being focused within the depth-of-field D centering on thefocus position A₂ in the direction along the second high-magnificationoptical path 52, that is, in the Z direction, i.e., the heightdirection. The depth-of-field D centering on the focus position A₁provides a subject imaging range 67 in the second high-magnificationoptical path 52, and the common imaging element 31 can image subjectswithin the subject imaging range 67.

Since both the first and second high-magnification optical paths 51 and52 pass through the same high-magnification lens 34, the depth-of-fieldsD of the respective high-magnification optical paths 51 and 52 have anequal range. The distance dZ between the focus positions A₁ and A₂depends on the difference in the distance from the high-magnificationlens 34 to the imaging plane 36 between the high-magnification opticalpaths 51 and 52. According to the exemplary embodiment of the presentinvention, dZ is set to be equal to the depth-of-field D, as shown inFIG. 5.

In contrast, as shown in FIG. 5, the low-magnification optical path 53uses the low-magnification lens 35 with a magnification lower than thatof the high-magnification lens 34 for imaging. Since lower-magnificationlenses have larger depth-of-fields, the low-magnification lens 35 has adepth-of-field E larger than that of the high-magnification lens 34, andimaging subjects can be imaged on the imaging plane 38 with beingfocused within the depth-of-field E centering on the focus position A₃in the direction along the low-magnification optical path 53, that is,in the Z direction, i.e., the height direction. The depth-of-field Ecentering on the focus position A₃ provides a subject imaging range 68in the low-magnification optical path 53. Since the depth-of-field E ofthe low-magnification lens 35 is large, the subject imaging range 68 inthe low-magnification optical path 53 includes the lead frame 61 and themulti-layered semiconductor chips 63 a, 63 b, and 63 c mounted on thelead frame.

FIG. 6 shows an example of a field of view 71 of the high-magnificationoptical system including the first and second high-magnification opticalpaths 51 and 52 and a field of view 72 of the low-magnification opticalsystem including the low-magnification optical path 53 on the lead frame61 and the semiconductor chips 63. As shown in FIG. 6, since thehigh-magnification optical system uses the high-magnification lens 34for imaging, the field of view 71 includes one corner of thesemiconductor chips 63. However, since the low-magnification opticalsystem uses the low-magnification lens 35 for imaging that has amagnification lower than that of the high-magnification lens 34, thefield of view 72 is wider than the field of view 71 of thehigh-magnification optical system. Although FIG. 6 shows a case wherethe field of view 72 of the low-magnification optical system includespart of the semiconductor chips 63 and several leads 62, leads 62 canonly be included depending on the position of the field of view.

FIG. 7 shows the field of view 71 of the high-magnification opticalsystem in the same size as the field of view 72 of the low-magnificationoptical system, where the field of view 71 of the high-magnificationoptical system includes pads 64 on the semiconductor chips 63 and aparticular pattern 65 imaged largely therein. As shown in FIG. 8, sincethe field of view 72 of the low-magnification optical system images alarger area than the high-magnification optical system within the samesized field of view, pads on the semiconductor chips 63 and leads 62arranged on the lead frame 61 are imaged smaller than in thehigh-magnification optical system.

The alignment between pads 64 on the semiconductor chips 63 and leads 62on the lead frame 61 using the above-described images taken by theimaging device 21 for bonding apparatus will be described below.

When the lead frame 61 with semiconductor chips 63 bonded thereon iscarried to a predetermined position along the guide rails 81 a and 81 bshown in FIG. 1, the imaging device 21 sets the position of the field ofview 72 of the low-magnification optical system to include several leads62 on the lead frame 61 as shown in FIG. 8, and the imaging element 33(see FIG. 3) outputs an image including the several leads 62 aselectrical signals for each pixel. The electrical signals for each pixelof the imaging element 33 is input to a control device not shown in thedrawings, and the control device detects the edges L₁₁ and L₁₂ of a lead621 that extend in the X direction by, for example, normalizedcorrelation processing. Then, the distances in the Y direction betweenthe center of the field of view 72 and the respective edges L₁₁ and L₁₂detected are obtained based on the difference in the number of pixelsbetween the pixel positions in the Y direction of the respective edgesL₁₁ and L₁₂ and the pixel position of the center of the field of view72. Similarly, the control device detects the leading end portion L₁₃ ofthe lead 621 that extends in the X direction by, for example, normalizedcorrelation processing, and then the distance between the center of thefield of view 72 and the leading end portion L₁₃ detected are obtainedbased on the difference in the number of pixels between the pixelposition in the X direction of the leading end portion L₁₃ and the pixelposition of the center of the field of view 72. The control device thusobtains the coordinate positions in the X and Y directions of theleading end of the lead 621 with respect to the center of the field ofview 72. Since the imaging device 21 is fixed to the bonding head 11 andthereby the coordinate position of the center of the field of view 72 inthe imaging device 21 with respect to the wire bonder 10 is known, thusobtaining the X and Y coordinate positions of the leading end of thelead 621 with respect to the center of the field of view 72 allows thecoordinate position of the leading end of the lead 621 with respect tothe entire wire bonder 10 to be obtained. Subsequently, the controldevice obtains the coordinate positions in the X and Y directions of theleading end of each of the several leads 62 with respect to the centerof the field of view 72 to obtain the coordinate position of the leadingend of each lead 62 with respect to the entire wire bonder 10.

After obtaining the coordinate positions in the X and Y directions ofthe leading end of each lead 62 included in the field of view 72 withrespect to the entire wire bonder 10, the imaging device 21 then movesto a position where the area adjacent to the field of view 72 in the Ydirection shown in FIG. 6 is included in the field of view, and thecoordinate position of the leading end of each lead 62 imaged in thenext field of view is obtained. The imaging device 21 repeats theseoperations sequentially to scan all the leads 62 around thesemiconductor chips 63 and thereby obtain the coordinate positions ofthe leading ends of all the leads 62. According to the exemplaryembodiment of the present invention, since the field of view 72 shown inFIG. 6 can include about one-third of the leads 62 arranged to face oneside of the semiconductor chips 63, only twelve different positions foreach field of view are required for imaging to obtain the coordinatepositions of all the leads 62 on the lead frame 61, which requires onlya significantly smaller number of captive images than in the case ofscanning each lead 62 using the field of view 71 of thehigh-magnification optical system shown in FIG. 6 to image all the leads62. The shown exemplary embodiment thereof thus has such an advantageouseffect that the time for imaging the lead frame 61 and therefore thetime for obtaining the coordinate positions of the leads 62 can bereduced to achieve high-speed wire bonding.

Next, the imaging device 21 for bonding apparatus sets the position ofthe field of view 71 of the high-magnification optical system to includethe particular pattern 65 in the corner of the semiconductor chips 63 asshown in FIG. 7, and the common imaging element 31 outputs an imageincluding the particular pattern 65 as electrical signals for eachpixel. The electrical signals for each pixel of the imaging element 31is input to the control device not shown in the drawings, and thecontrol device performs, for example, normalized correlation processingto obtain the distances in the X and Y directions between the center ofthe field of view 71 and the particular pattern 65 based on thedifference in the number of pixels between the pixel position of theparticular pattern 65 and the pixel position of the center of the fieldof view 72. Then, the X and Y coordinate positions of the particularpattern 65 are obtained with respect to the center of the field of view71 and therefore the wire bonder 10.

Next, the imaging device 21 moves to a position where the opposingcorner of the semiconductor chips 63 is included in the field of view toobtain the coordinate position of another particular pattern 65 in theopposing corner. Since pads 64 on the semiconductor chips 63 aremanufactured to have more accurate positions than leads 62 on the leadframe 61, obtaining the coordinate positions of the two opposingparticular patterns 65 to locate the coordinate positions of thesemiconductor chips 63 leads to locating the coordinate positions of thepads 64. This allows the coordinate positions of the pads 64 on thesemiconductor chips 63 to be obtained without detecting the position ofeach pad 64.

When obtaining the coordinate positions of the pads 64 on thesemiconductor chips 63, the first high-magnification optical path 51 isused if the position in the Z direction, i.e., the height direction ofeach pad 64 on the subject semiconductor chips 63 is within the subjectimaging range 66 in the first high-magnification optical path 51 shownin FIG. 5, while the second high-magnification optical path 52 is usedif the position in the Z direction of each pad 64 on the subjectsemiconductor chips 63 is within the subject imaging range 67 in thesecond high-magnification optical path 52 shown in FIG. 5. The first andsecond high-magnification optical paths 51 and 52 are switched byrotating the motor 91 in the shutter 90 shown in FIG. 3. The selectionof which optical path to be used for imaging can be based on thethickness, the number of levels, and the step to be imaged, etc., of thesemiconductor chips 63 to be subject to wire bonding, can be preset by aprogram or the like for the wire bonding step, or can be made so thatthe boundary of the imaging subject can be identified more clearly byprocessing images taken through the first and second high-magnificationoptical paths 51 and 52. Then, if the semiconductor chips 63 are stackedin multiple layers as shown in, for example, FIG. 5, the firsthigh-magnification optical path 51 is used by operating the shutter 90so that the first high-magnification optical path 51 is opened while thesecond high-magnification optical path 52 is closed to image thesemiconductor chips 63 a and 63 b and obtain the coordinate positions ofthe pads 64 a and 64 b in the first and second layers belonging to thesubject imaging range 66 far from the high-magnification lens 34, whilethe second high-magnification optical path 52 is used by operating theshutter 90 so that the second high-magnification optical path 52 isopened while the first high-magnification optical path 51 is closed toimage the semiconductor chip 63 c and obtain the coordinate position ofthe pad 64 c in the third layer belonging to the subject imaging range67 centering on the focus position A₂ close to the high-magnificationlens 34. Since the exemplary embodiment of the present invention thusincludes two high-magnification optical paths 51 and 52, images within alarge subject imaging range in the Z direction, i.e., the heightdirection can be taken with no lens shift while using thehigh-magnification lens 34 during wire bonding in such multi-layeredsemiconductor chips as shown in FIG. 5 with a great difference in levelin the Z direction, i.e., the height direction, so that thesemiconductor chips 63 a, 63 b, and 63 c with a great difference inlevel in the height direction can be imaged accurately. The exemplaryembodiment thereof can also switch two high-magnification optical paths,the first and second high-magnification optical paths 51 and 52, by theshutter 90 to use the imaging element 31 commonly, so that the systemcan be simplified.

After obtaining the coordinate position of the leading end of each lead62 and the coordinate position of each pad 64 through the foregoingoperations, the wire bonder 10 operates the bonding head 11 and theZ-direction drive mechanism 18 shown in FIG. 1 to drive the capillary 14in the X, Y, and Z directions that is fixed to the leading end of theultrasonic horn 13 and thereby to bond the wire 16, which is insertedthrough the capillary 14, between each pad 64 on the semiconductor chips63 and each lead 62 on the lead frame 61 shown in FIG. 5.

Then, when all the pads 64 on one set of semiconductor chips 63 havecompletely been connected to leads 62 on the lead frame 61 through wires16, the lead frame 61 is carried so that the next set of semiconductorchips 63 are brought to the bonding position. The imaging device 21scans images of the lead frame 61 again to obtain the coordinateposition of each lead 62 and the coordinate position of each particularpattern 65 on the semiconductor chips 63 for the next wire bonding.

As seen from the above, the imaging device 21 according to theabove-described exemplary embodiment of the present invention, whichscans each lead 62 through the low-magnification optical system with awide field of view to image all the leads 62, requires a small number ofcaptive images; accordingly, the time for imaging the lead frame andtherefore the time for obtaining the coordinate positions of the leads62 can be reduced to achieve high-speed wire bonding. In addition, sincethe two high-magnification optical paths 51 and 52 are provided in thehigh-magnification optical system, images within a large subject imagingrange in the height direction can be taken with no lens shift whileusing the high-magnification lens 34 during wire bonding inmulti-layered semiconductor chips with a great difference in level inthe height direction, so that the semiconductor chips 63 a, 63 b, and 63c with a great difference in level in the height direction can be imagedaccurately.

Although in the above-described exemplary embodiment of the presentinvention, the high-magnification optical system includes twohigh-magnification optical paths, more high-magnification optical pathscan be provided so as to correspond to the difference in level of thesemiconductor chips 63. Although the exemplary embodiment of the presentinvention describes imaging the lead frame 61 and the semiconductorchips 63 mounted on the lead frame 61, it can also be applied to a caseof imaging a substrate such as a BGA (Ball Grid Array) package andsemiconductor chips 63 mounted on a substrate.

Next will be described another exemplary embodiment of the presentinvention with reference to FIG. 9. Components identical with those inthe exemplary embodiment thereof described with reference to FIG. 3 aredesignated by the same reference numerals to omit descriptions thereof.The imaging device 21 for bonding apparatus according to the exemplaryembodiment thereof includes as seen from FIG. 2: an introduction section22 for introducing light from the subject semiconductor chips 63 or leadframe 61 therethrough; a tube framework 23 incorporating opticalcomponents such as lenses and mirrors to guide light incident throughthe introduction section 22; and cameras 24 and 26 including imagingelements attached to the tube framework 23 to receive light through thetube framework 23 as shown in FIG. 2, as is the case in theabove-described exemplary embodiment thereof.

As shown in FIG. 9, the imaging device 21 for bonding apparatusaccording to the exemplary embodiment of the present invention has ahigh-magnification optical system as a first optical system and alow-magnification optical system as a second optical system. Thehigh-magnification optical system includes: a first high-magnificationoptical path 51 extending from the subject semiconductor chips 63 orlead frame 61 to an imaging plane 36 through the introduction section22, a subject side lens 45 and a half mirror 41, a first imaging planelens 46 and a half mirror 42 a, a shutter 90, and a half mirror 42 b;and a second high-magnification optical path 52 extending from thesubject semiconductor chips 63 or lead frame 61 to the common imagingplane through the introduction section 22, subject side lens 45 and halfmirror 41, first imaging plane lens 46, reflected at the half mirror 42a to branch from the first high-magnification optical path 51, reflectedat a mirror 43 a to pass through the shutter 90, and reflected at amirror 43 b and the half mirror 42 b to join the firsthigh-magnification optical path. The low-magnification optical systemincludes: a low-magnification optical path 53 extending from the subjectsemiconductor chips 63 or lead frame 61 to an imaging plane 38 throughthe introduction section 22, subject side lens 45, reflected at the halfmirror 41 between the subject side lens 45 and the first imaging planelens 46 to branch from the high-magnification optical system, andreflected at a mirror 44 to pass through a second imaging plane lens 47.

The subject side lens 45 and the first imaging plane lens 46 form ahigh-magnification total, while the subject side lens 45 and the secondimaging plane lens 47 form a low-magnification total having a lowertotal magnification than the high-magnification total formed by thesubject side lens 45 and the first imaging plane lens 46. The subjectside lens 45 and the first and second imaging plane lenses 46 each canalso be a single lens or a group of lenses in which multiple lenses arecombined to correct aberration. The configurations of the imagingelements 31 and 33 provided on the respective imaging planes 36 and 38and the shutter 90 are the same as in the exemplary embodiment of thepresent invention described heretofore with reference to FIG. 3.

The high-magnification optical system substantially has onehigh-magnification total formed by the subject side lens 45 and thefirst imaging plane lens 46. Accordingly, the distance S′ between thelens L and the imaging plane on the imaging plane side of the lensdescribed in FIG. 4 corresponds to the distance between the firstimaging plane lens 46 and the imaging plane 36. Accordingly, the secondhigh-magnification optical path 52, in which the distance from the firstimaging plane lens 46 to the imaging plane 36 is greater than in thefirst high-magnification optical path 51 and thereby the distance fromthe high-magnification total to the imaging plane 36 is greater than inthe first high-magnification optical path 51, has a focus position A₂where the distance from the subject side lens 45 in the front of thehigh-magnification total to the subject semiconductor chips 63 issmaller than in the first high-magnification optical path 51. Incontrast, the first high-magnification optical path 51, in which thedistance from the first imaging plane lens 46 to the imaging plane 36 issmaller than in the second high-magnification optical path 52 andthereby the distance from the high-magnification total to the imagingplane 36 is smaller than in the second high-magnification optical path52, has a focus position A₁ where the distance from the subject sidelens 45 in the front of the high-magnification total to the subjectsemiconductor chips 63 is greater than in the second high-magnificationoptical path 52.

The low-magnification optical system is the same as in theabove-described exemplary embodiment of the present invention exceptthat it includes the second imaging plane lens 47 having a lower totalmagnification with the subject side lens 45, which is used commonly withthe high-magnification optical system, than the high-magnificationtotal.

The alignment method between pads 64 on the semiconductor chips 63 andleads 62 on the lead frame 61 using images taken by the imaging device21 for bonding apparatus according to the exemplary embodiment of thepresent invention is the same as in the above-described exemplaryembodiment thereof.

In addition to the same advantageous effects as in the above-describedexemplary embodiment of the present invention, the exemplary embodimentthereof, in which each optical system includes a total formed by thesubject side lens 45 and the first or second imaging plane lens 46 or47, exhibits an advantageous effect that the length of the entireoptical systems can be reduced to provide a space-saving imaging device21 for bonding apparatus.

The exemplary embodiment of the present invention, which describes thecase of imaging the lead frame 61 and the semiconductor chips 63 mountedon the lead frame 61, can be applied to the case of imaging a substratesuch as a BGA package and semiconductor chips 63 mounted on thesubstrate. The substrate can also include a tape with leads printedthereon.

Still another exemplary embodiment of the present invention will bedescribed with reference to FIG. 10. Components identical with those inthe exemplary embodiments thereof described with reference to FIGS. 3and 9 are designated by the same reference numerals to omit descriptionsthereof.

In the exemplary embodiment of the present invention, the firsthigh-magnification optical path 51, which extends to an imaging plane 36through a shutter and reflected at a mirror 43 b and a half mirror 42 b,includes a glass plate 48 as optical path length adjustment meansinstalled between the mirror 43 b and the half mirror 42 b. The secondhigh-magnification optical path 52 also extends to the common imagingplane 36 through the shutter 90 and half mirror 42 b, and joining thefirst high-magnification optical path 51. In the exemplary embodimentthereof, the optical path lengths of the first high-magnificationoptical path 51 with no glass plate 48 and the second high-magnificationoptical path 52 would be approximately the same, and the difference inthe optical path length between the two high-magnification optical paths51 and 52 is adjusted by the glass plate 48. The optical path lengthadjustment means is not restricted to such a glass plate 48, but can bea plastic plate or an auxiliary lens or the like. Then, adjusting theposition in the direction along the first high-magnification opticalpath and/or the shape such as thickness of the glass plate 48 allows thefocus position A₁ of the first high-magnification optical path 51 andthe position of the subject imaging range 66 to be adjusted in thedirection along the first high-magnification optical path 51, that is,in the Z direction, i.e., the height direction shown in FIG. 5, so thatthe distance dZ between the subject imaging range 66 in the firsthigh-magnification optical path 51 and the subject imaging range 67 inthe second high-magnification optical path 52 can be set so that thesubject imaging ranges 66 and 67 are arranged to be overlapped with eachother or to have a clearance therebetween.

Although the above-described exemplary embodiments of the presentinvention describe the case of applying the imaging device for bondingapparatus to the wire bonder 10, the present invention can be applied toother bonding apparatuses such as die bonders, flip-chip bonders, andtape bonders.

1. An imaging device for a bonding apparatus for imaging imaging subjectand multi-layered semiconductor chips mounted on said imaging subject,comprising: a first optical system having a plurality of optical pathsthat extend to a common imaging plane through a first lens and havedifferent optical path lengths from said first lens to said commonimaging plane correspondingly to a plurality of subject imaging rangesat different distances from said first lens; an optical path switchingmeans for opening one of said plurality of optical paths in said firstoptical system and closing another one of said optical paths; a secondoptical system branching from said first optical system on a subjectside of said first lens and having an optical path that extends to animaging plane through a second lens with a lower magnification than saidfirst lens, said second optical system having a field of view wider thanthat of said first optical system; a first imaging element provided onsaid common imaging plane in said first optical system to image eachlayer of said multi-layered semiconductor chips mounted on said imagingsubject; a second imaging element provided on said imaging plane in saidsecond optical system to image said imaging subject.
 2. An imagingdevice for a bonding apparatus for imaging imaging subject andmulti-layered semiconductor chips mounted on said imaging subject,comprising: a first optical system having a plurality of optical pathsthat extend to a common imaging plane through a subject side of the lensand a first imaging plane lens and have different optical path lengthsfrom said first subject side of the lens to said common imaging planecorrespondingly to a plurality of subject imaging ranges at differentdistances from said subject side of the lens; an optical path switchingmeans for opening one of said plurality of optical paths in said firstoptical system and closing another one of said optical paths; a secondoptical system branching from said first optical system between saidsubject side of the lens and said first imaging plane lens and having anoptical path that extends to an imaging plane through a second imagingplane lens having a lower total magnification with said subject side ofthe lens than said first imaging plane lens said second optical systemhaving a field of view wider than that of said first optical system; afirst imaging element provided on said common imaging plane in saidfirst optical system to image each layer of said multi-layeredsemiconductor chips mounted on said imaging subject; a second imagingelement provided on said imaging plane in said second optical system toimage said imaging subject.
 3. The imaging device for a bondingapparatus according to claim 1, wherein said optical path switchingmeans is configured to switch said plurality of optical paths inaccordance with a height position of each layer of said multi-layeredsemiconductor chips to be imaged.
 4. The imaging device for a bondingapparatus according to claim 2, wherein said first optical system has anoptical path length adjustment means installed in each optical pathbetween said first imaging plane lens and each imaging plane, said meansbeing positioned variably in a direction along each optical path.
 5. Theimaging device for bonding apparatus according to claim 4, wherein saidoptical path length adjustment means is an optical path lengthadjustment lens, said optical path length adjustment lens is made of oneselected from the group consisting of a light transmitting glass, alight transmitting plastic, and a light transmitting ceramic.
 6. Animaging methods of imaging imaging subject and multi-layeredsemiconductor chips mounted on said imaging subject using an imagingdevice for a bonding apparatus, comprising the steps of: providing animaging device for a bonding apparatus, said imaging device comprising:a first optical system having a plurality of optical paths that extendto a common imaging plane through a first lens and have differentoptical path lengths from said first lens to said common imaging planecorrespondingly to a plurality of subject imaging ranges at differentdistances from said first lens, an optical path switching means foropening one of said plurality of optical paths in said first opticalsystem and closing another one of said optical paths, a second opticalsystem branching from said first optical system on the imaging planeside of said first lens and having an optical path that extends to animaging plane through a second lens with a tower magnification than saidfirst lens, said second optical system having a field of view wider thanthat of said first optical system, and a first imaging element providedon said common imaging plane in said first optical system and a secondimaging element provided on said imaging plane in said second opticalsystem; a lead image imaging step of scanning the field of view of saidsecond optical system on said imaging subject to cause said secondimaging element provided on said imaging plane in said second opticalsystem to image said imaging subject including leads around an entirecircumference of said multi-layered semiconductor chips; and asemiconductor chip imaging step of, using said first imaging element insaid first optical system imaging each layer of said multi-layeredsemiconductor chips provided on said imaging plane in said first opticalsystem through said one optical path in said first optical system thatis opened by said optical path switching means in accordance with aheight position of each layer of said multi-layered semiconductor chips.7. An imaging method of imaging, imaging subject and multi-layeredsemiconductor chips mounted on said imaging subject using an imagingdevice for a bonding apparatus, comprising the steps of: providing animaging device for a bonding apparatus, said imaging device comprising:a first optical system having a plurality of optical paths that extendto a common imaging plane through a subject side of the lens and a firstimaging plane lens and have different optical path lengths from saidfirst imaging plane lens to said common imaging plane correspondingly toa plurality of subject imaging ranges at different distances from saidsubject side of the lens, an optical path switching means for openingone of said plurality of optical paths in said first optical system andclosing another one of said optical paths, a second optical systembranching from said first optical system between said subject side ofthe lens and said first imaging plane lens and having an optical paththat extends to an imaging plane through a second imaging plane lenshaving a lower total magnification with said subject side of the lensthan said first imaging plane lens, said second optical system having afield of view wider than that of said first optical system, a firstimaging element provided on said common imaging plane in said firstoptical system, and a second imaging element provided on said imagingplane in said second optical system; a lead image imaging step ofscanning the field of view of said second optical system on said imagingsubject to cause said second imaging element provided on said imagingplane in said second optical system to image said imaging subjectincluding leads around an entire circumference of said multi-layeredsemiconductor chips; a semiconductor chip imaging step of, using saidfirst imaging element in said first optical system, imaging each layerof said multi-layered semiconductor chips provided on said imaging planein said first optical system through said one optical path in said firstoptical system that is opened by said optical path switching means inaccordance with a height position of each layer of said multi-layeredsemiconductor chips.
 8. The imaging device for a bonding apparatusaccording to claim 1, wherein said imaging subject is one selected fromthe group consisting of a lead frame and a substrate.
 9. The imagingdevice for a bonding apparatus according to claim 2, wherein saidimaging subject is one selected from the group consisting of a leadframe and a substrate.
 10. The imaging device for a bonding apparatusaccording to claim 2, wherein said optical path switching means isconfigured to switch said plurality of optical paths in accordance witha height position of each layer of said multi-layered semiconductorchips to be imaged.
 11. The imaging method according to claim 6, whereinsaid imaging subject is one selected from the group consisting of a leadframe and a substrate.
 12. The imaging method according to claim 7,wherein said imaging subject is one selected from the group consistingof a lead frame and a substrate.